Border treatment of composite metal plate surface heating unit

ABSTRACT

A low thermal mass, solid plate surface heating unit having a top utensil-supporting surface of composite metal of high thermal conductivity and corrosion and oxidation resisting materials. A metal sheathed electrical resistance heating element is pressed against the underside of the composite plate by a back-up plate. There are two modifications of the manner of spacing the peripheral edge of the inner core of the composite metal plate back from the peripheral edge of the heating unit. In one modification, a margin of the inner core and the bottom skin are cut away so as to be set back from the peripheral edge of the top skin. In the second modification, the top and bottom skins of the composite plate are sealed over the edge of the inner core. Then the peripheral edge of the back-up plate is brought out beyond the peripheral edge of the composite plate and a trim strip is wrapped around the edge of the back-up plate and the edge of the top skin and sealed therebetween.

United States Patent 1191 Hurko et al.

[111 3,826,898 1451 July 30, 1974 15 BORDER TREATMENT OF COMPOSITE3,622,754 11/1971 Hurko 219/462 I METAL PLATE SURFACE HEATING UNIT3,781,522 3/1972 Borom et al. 219/462 [75] Inventors: 5 33 g i i fiPrimary E.raminer-Volodymyr Y. Mayewsky o O Oulsv' Attorney, Agent, orFirm-Richard L. Czlslin [73] Assignee: General Electric Company,

LOulSVllle, Ky. 57 ABSTRACT Filedi 1973 A low thermal mass, solid platesurface heating unit 21 A N 419 593 having a top utensil-supportingsurface of composite 1 pp 0 metal of high thermal conductivity andcorrosion and oxidation resisting materials. A metal sheathed electrilCl 2l9/436, cal resistance heating element is pressed against the 219/61, 219/463, 2 9/ 2l9/530 underside of the composite plate by a back-upplate. [5 l Int. Cl. H05b 3/68 Th e two modifications of the manner ofspacing Field S the peripheral edge of the inner core of the composite219/441, 458, 459, 460, 461, 462, 63, metal plate back from theperipheral edge of the heat- 530, 540 ing unit. In one modification, amargin of the inner core and the bottom skin are cut away so as to beset References Clled back from the peripheral edge of the top skin. Inthe UNlTED STATES PATENTS second modification, the top and bottom skinsof the 2,443,806 6/1948 Shaftcr 219/436 composite Plate are Sealed Overthe edge of the inner 2,570,975 /1951 04161116111 219/459 Cow Then thePeripheral edge Of the P Plate is 2,969,452 1/1961 Geller et al. 219/437X brought out beyond the peripheral edge of the com- 3,097,21l9 7/1963Clark 219/442 UX posite plate and a trim strip is wrapped around the3.316.390 4/1967 Gflugler 6t 219/464 edge of the back-up plate and theedge of the top skin BaSSclt, Jr. et a]. and 3,445,630 5/1969 Ulum219/438 3,569,672 3/1971 Hurko 219/464 9 Claims, 2 Drawing Figures 32 4547 l8 l2. lo

l 1 j(/ I I I. 7.\ 1G 58 3 4 52 Z, Z6 (64 BORDER TREATMENT OF COMPOSITEMETAL PLATE SURFACE HEATING UNIT BACKGROUND OF THE INVENTION For manyyears, electric surface cooking has been performed on metal sheathedelectrical resistance heating elements of spiral configurations.However, in many foreign countries electric surface cooking is performedmostly on cast iron solid plate units where the resistance heatingelements are either embedded therein or permanently fastened thereto.

One important advantage of a solid plate surface heating unit is itsease of cleanability, since it forms with the cooktop in which the unitis mounted a solid surface. Hence, there are no holes in the cooktopthrough which spillovers and boilovers may leak and become difficult toreach for cleaning up. One important shortcoming of the cast ironsurface unit plates is their high thermal mass and slow heat-up andcooldown rates, as well as their somewhat unattractive coloration.

An important advance in the art of solid plate surface heating units wasintroduced in U.S. Pat. No. 3,569,672 of Bohdan Hurko entitled LOWTHERMAL MASS, PLATE SURFACE HEATING UNIT. This patent taught the use ofa composite metal plate for the utensil-supporting surface of a solidplate surface heating unit for distributing the heat rapidly anduniformly over the plate.

One modification of the present invention is illustrated in co-pendingpatent application of Bohdan Hurko Ser. No. 419,592 entitled COMPOSITEMETAL PLATE SURFACE HEATING UNIT which is being filed concurrentlyherewith. The invention in that copending application relates to amethod of holding a metal sheathed electrical resistance heating elementin contact with the underside of a composite plate by means of anembossed back-up plate so as to allow limited sliding movement betweenthe heating element and the composite plate, and thereby prevent warpageof the composite plate.

A principal object of the present invention is to provide a compositemetal plate surface heating unit with means to set back the peripheraledge of the inner core of the composite metal plate from the peripheraledge of the heating unit so as to reduce the conduction of heat from theheating unit to its supporting surface.

A further object of the present invention is to provide a compositemetal plate surface heating unit with an effective manner of sealing offthe inner core of the composite metal plate and at the same time reducethe conduction of heat from the heating unit to its supporting surface.

SUMMARY OF THE INVENTION The present invention, in accordance with oneform thereof, relates to a low thermal mass, solid plate surface heatingunit comprising a thin plate of composite metal that has high thermalconductivity, and is also strong and oxidization and corrosionresistant. A metal sheathed electrical resistance heating element ofcoiled configuration is pressed against the underside of the compositemetal plate. A back-up plate serves to press the heating element againstthe underside of the composite metal plate. The periphery of the back-upplate extends out beyond the extremity of the inner core of thecomposite metal plate, and a trim strip bridges the edge of the back-upplate and the edge of the composite plate and is sealed therebetween.

BRIEF DESCRIPTION OF THE DRAWINGS This invention will be betterunderstood from the following description taken in conjunction with theaccompanying drawings and its scope will be pointed out in the appendedclaims.

FIG. I is a cross-sectional elevational view through the center of asolid plate surface heating unit embodying the present invention,wherein the unit is shown mounted in an opening in a cooktop by means ofspring clips that engage the edge of the opening.

FIG. 2 is a fragmentary cross-sectional elevational view of a secondmodification of the present invention relating to another method ofsealing the core of the composite metal plate and insulating the edge ofthe heating unit so as to reduce the conduction of heat to thesupporting surface.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Turning now to a considerationof the drawings, and in particular to FIG. I, there is shown acrosssectional elevational view of a solid plate surface heating unit 10embodying the present invention having a top utensilsupporting plate 12formed of thin composite metal of high thermal conductivity with acenter core 14 of material such as copper, silver, or aluminum fordistributing the heat. rapidly over the entire plate and obtaining agenerally uniform temperature distribution. Copper has very low strengthat temperatures ranging in the vicinity of 1,400F and also it oxidizesvery readily. Since this copper sheet 14 is of small thickness, on theorder of 0.040 inches, it would also tendto warp easily under normalconditions due to thermal stress caused by uneven temperaturedistribution when using cooking utensils with warped bottom plates, andalso due to the high temperatures to which it is exposed.

The copper core 14 is sandwiched between two thin, integral stainlesssteel skins l5 and 16, each of a thickness of about 0.016 inches. Thestainless steel skins l5 and 16, being bonded to the outer surfaces ofthe composite plate provide strength to the plate. Such a plate wouldhave only slightly lower strength than a solid stainless steel plate ofa similar thickness. The composite metal plate 12 resists warpagebecause it combines high strength with high heat diffusivity, which nosingle material known to us is able to provide. The thin composite sheetmaterial 12 of central copper core 14 and two outer stainless steelskins 15 and 16 may be formed of individual sheets that are area weldedtogether as by a process of explosive welding which causes a bonding ofthe metal sheets along their entire mating surfaces.

The heat source for this solid plate surface heating unit 10 is a metalsheathed electrical resistance heating element 18 of spiralconfiguration that is flattened on its topside and pressed into tightcontact with the underside of the composite plate 12. Sheathed heatingelements such as this have a helical resistance wire embedded in a layerof magnesium oxide which is in turn covered by a metal sheath. Thisheating element 18 is of spiral configuration that is arranged in asingle plane, and its terminals 20 and 22 are folded down to lieadjacent to each other at one side of the surface unit, as is clearlyseen in FIG. 1.

Located beneath the heating element 18 is an embossed back-up plate 24of stainless steel or the like, which is fashioned from a flat sheetthat is stamped with a spiral recess 26 which closely overlies thespiral heating element 18. Moreover, the back-up plate 24 has smallaccess openings 27 for receiving the heating element terminals 20 and 22therethrough. A more complete description of the nature of this back-upplate is given in the co-pending patent application of Bohdan Hurko Ser.No. 4l9,592, which was cited above. The back-up plate 24 is providedwith a deep-drawn bowl formation 38 adjacent to Center thereof whichincludes a series of radial embossments 28 that terminate adjacent theoutermost turn of the spiral recess 26 for strengthening the overallassembly of the heating unit.

The area of the back-up plate 24 on both sides of the outermost turn ofthe spiral recess 26 which received the heating element 18, is in directcontact with the underside of the composite plate 12. These areas areidentified by the numerals 32 and 34, and they are permanently attachedto the underside of composite sheet 12 as by spot welding at widelyspaced points.

It must be understood that if the peripheral edge of the copper core 14were exposed to the atmosphere under high temperature conditions, itwould tend to corrode and oxidize rapidly thereby resulting in prematurefailure of the surface unit. Moreover, it is important to restrict thecondition of heat from the surface unit to the supporting cooktop 45 inwhich the surface unit 10 is mounted. Thus, it is well to stop thecopper core 14 short of making thermal contact with the cooktop 45. Inthe first modification of FIG. 1, this is done by cutting away orotherwise removing an annular strip or margin of the bottom skin 16 andthe copper core 14 for a distance of about one-half inch thereby leavingonly the top skin in that area identified by the numeral 47. Thisannular strip 47 is then seam welded between the top skin 15 of thecomposite plate 12 and the back-up plate 24. The peripheral edge of thisannular strip 47 is in turn sealed by a folded-over trim strip 49 ofmonel metal or the like that may also be seam welded to the mating partsso that the copper core 14 is well sealed within the composite plate 12.

Another element of this solid plate surface heating unit 10 is acircular reflector pan 51 of deep-drawn configuration that is assembledbeneath the composite metal sheet 12 and out of contact with the back-upplate 24 except adjacent the peripheral edge of the composite sheet 12and the reflector pan 51 as at 52. The edge of the reflector pan 51 iscovered by an asbestos gasket 54 which serves to hold the reflector pan51 away from the adjacent surface of the cooktop 45 as well as supportsthe entire heating unit thereby holding the composite sheet 12 up off ofthe cooktop as well as holding the trim strip 49 out of direct contactwith the cooktop 45. This insulating gasket 54 is important because italso serves as a sealing means between the cooktop 45 and the heatingunit 10, and finally serves as a heat transfer barrier between thecooktop and heating unit.

This reflector pan 51 is assembled with the other parts of the heatingunit 10 by a single bolt 56 located adjacent the center of the back-upplate 24 and integral therewith. The bolt 56 has a head 58 that islocated within the back-up plate 24 and is welded in this plate. Thebolt 56 is threaded and a nut 60 is slipped over the end of the bolt andtightened to hold the reflector pan 51 firmly in place. Notice that thereflector pan 5] has small access openings 62 that are generally alignedwith the openings 27 in the back-up plate 24 for receiving the heatingelement terminals 20 and 22 therethrough, so thatelectrical connectionsmay be made to the heating element 18 externally of the heating unit 10.

The cooktop 45 is provided with a recessed circular opening 64 forreceiving the heating unit 10 therein. An annular recessed ledge 66surrounds the recessed opening 64 and serves as the support means forthe peripheral edge of the reflector pan 51 such that the top surface ofthe composite plate 12 is almost flush with top surface of the cooktop45. A plurality of spring clips 68 are attached to the underside of thereflector pan 51 for engaging the edge of the opening 64 and holding theheating unit 10 firmly in place.

In the second modification of the present invention shown in FIG. 2wherein like elements are given the same reference numeral exceptprimed, as in the first modification of FIG. 1, there is a heating unit70 having a top plate 12 formed of thin composite metal with a centercore 14 such as copper, silver or aluminum, that is sandwiched betweentwo thin, integral stainless steel skins l5 and 16.

The heat source for this second modification is a metal sheathedelectrical resistant heating element 18' that is held in place by aback-up plate 24. The composite metal plate 12' is placed in a pinch dieof a punch press of large force capability which forms an outer strip ofthe composite plate 12' into a tapered edge that is beveled downwardwhere in effect the outermost edge of the inner core material 14 isreduced merely to a fine line separating the top skin 15 from the bottomskin 16. The periphery of the back-up plate 24 extends outwardly beyondthe extremity of the composite sheet 12' as at 72. This annularextension 72 of the back-up plate is stepped up in order to have it liein substantially the same plane as the tip of the composite sheet 12'.Then a wide wrap-around trim strip 74 of monel metal or the like isfitted between the peripheral edge of the back-up plate and theperipheral edge of the composite sheet 12 by having the lower flange 76underlying the back-up plate 24 and a top flange 77 bridging the gapbetween the back-up plate and the composite sheet 12 with an edge 78that is in engagement with the top surface of the composite sheet 12.This trim strip 74 may either be seam welded in place or it may becrimped in place to form a substantial finished product.

Modifications of this invention will occur to those skilled in this art;therefore, it is to be understood that this invention is not limited tothe particular embodiments disclosed, but that it is intended to coverall modifications which are within the true spirit and scope of theinvention as claimed.

What is claimed as new and desired to be Letters Patent of the UnitedStates is:

l. A low thermal mass, solid plate surface heating unit comprising athin composite metal plate having a core of high thermal conductivityselected from the group comprising copper, silver, and aluminum, and anouter skin of rigid and oxidation and corrosion resisting materialsealing the core and selected from the group comprising stainless steel,nickel, and chromium, a

secured by metal sheathed electrical resistance heating element heldagainst the underside of the composite plate to serve as the heat sourcefor the composite plate, a metal back-up plate beneath the heatingelement for holding the heating element against the composite plate, theperiphery of the back-up plate extending outwardly beyond the extremityof the core of the composite plate by a wide margin so as to reduce theconduction of heat from the heating unit to its supporting surface, anda metal trim strip wrapped around the edge of the back-up plate and thetop skin of the composite plate and sealed therebetween.

2. A low thermal mass, solid plate surface heating unit comprising athin composite metal plate having a core of high thermal conductivityselected from the group comprising copper, silver, and aluminum, and anouter skin of rigid and oxidation and corrosion resisting materialsealing the core and selected from the group comprising stainless steel,nickel, and chromium, a metal sheathed electrical resistance heatingelement held against the underside of the composite plate to serve asthe heat source for the composite plate, a metal back-up plate beneaththe heating element for holding the heating element against thecomposite plate, the periphery of the back-up plate extending out beyondthe extremity of the composite plate by a wide margin so as to reducethe conduction of heat from the heating unit to its supporting surface,and a metal trim strip bridging the edge of the back-up plate and theedge of the composite plate and sealed thereto.

3. A composite metal plate surface heating unit as recited in claim 2with the addition of a reflector pan assembled beneath the back-upplate, the peripheral edge of the reflector pan being provided with aninsulating gasket means which is sandwiched between the reflector panand back-up plate and serves as a heat transfer barrier therebetweensaid gasket means also being adapted to serve as the support means ofthe heating unit on a support surface and thereby adapted to serve as asealing means therebetween and to prevent direct contact of thecomposite plate with the support surface.

4. A composite metal plate surface heating unit having a thin multilayercomposite metal sheet as its top utensil-supporting surface, saidcomposite sheet having an inner heat spreading core of non-ferrousmetallic alloy of high thermal conductivity, the core being sealed in anouter metallic alloy skin of higher strength and resistance to oxidationthan the inner core, a metal sheathed electrical resistance heatingelement pressed against the underside of the composite sheet to serve asthe heat source for the heating unit, a metal back-up plate beneath theheating element for holding the heating element in place, the peripheryof the back-up plate extending outwardly beyond the extremity of theinner core by a wide margin so as to reduce the conduction of heat fromthe heating unit to its supporting surface, and a metal trim encirclingthe heating unit and sealed between the edge of the top skin of thecomposite sheet and to the edge of the back-up plate so as to stop theheat spreading core short of the periphery of the heating unit andreduce the conduction of heat from the inner core to the peripheralextremity of the heating unit.

5. A composite metal plate surface heating unit as recited in claim 4wherein the extent of the bottom skin of the composite sheetsubstantially coincides with the extent of the inner core, and thediameter of the top skin substantially equals the diameter of theback-up plate.

6. A composite metal plate surface heating unit as recited in claim 5with the addition of a reflectorpan assembled beneath the back-up plate,the peripheral edge of the reflector pan being provided with aninsulating gasket means which is sandwiched between the reflector panand back-up plate and serves as a heat transfer barrier therebetweensaid gasket means also being adapted to serve as the support means ofthe heating unit on a support surface and thereby adapted to serve as asealing means therebetween and to prevent direct contact of thecomposite plate with the support surface.

7. A composite metal plate surface heating unit as recited in claim 4wherein a narrow annular margin of both the bottom skin and the innercore has been removed from the top skin so that the periphery of theinner core is set back from the periphery of the heating unit.

8. A composite metal plate surface heating unit as recited in claim 4wherein the periphery of the composite sheet is pressed into a taperedbevelled edge, a narrow strip of the periphery of the back-up plate isformed to lie in substantially the same plane as the bevelled edge ofthe composite sheet, whereby the said trim strip serves as an extensionof the composite sheet.

9. A composite metal plate surface heating unit as recited in claim 8with the addition ofa reflector pan assembled beneath the back-up plate,the peripheral edge of the reflector pan being provided with aninsulating gasket means which is sandwiched between the reflector panand back-up plate and serves as a heat transfer barrier therebetweensaid gasket means also being adapted to serve as the support means ofthe heating unit on a support surface and thereby adapted to serve as asealing means therebetween and to prevent direct contact of thecomposite plate with the support surface.

1. A low thermal mass, solid plate surface heating unit comprising athin composite metal plate having a core of high thermal conductivityselected from the group comprising copper, silver, and aluminum, and anouter skin of rigid and oxidation and corrosion resisting materialsealing the core and selected from the group comprising stainless steel,nickel, and chromium, a metal sheathed electrical resistance heatingelement held against the underside of the composite plate to serve asthe heat source for the composite plate, a metal back-up plate beneaththe heating element for holding the heating element against thecomposite plate, the periphery of the back-up plate extending outwardlybeyond the extremity of the core of the composite plate by a wide marginso as to reduce the conduction of heat from the heating unit to itssupporting surface, and a metal trim strip wrapped around the edge ofthe back-up plate and the top skin of the composite plate and sealedthereBetween.
 2. A low thermal mass, solid plate surface heating unitcomprising a thin composite metal plate having a core of high thermalconductivity selected from the group comprising copper, silver, andaluminum, and an outer skin of rigid and oxidation and corrosionresisting material sealing the core and selected from the groupcomprising stainless steel, nickel, and chromium, a metal sheathedelectrical resistance heating element held against the underside of thecomposite plate to serve as the heat source for the composite plate, ametal back-up plate beneath the heating element for holding the heatingelement against the composite plate, the periphery of the back-up plateextending out beyond the extremity of the composite plate by a widemargin so as to reduce the conduction of heat from the heating unit toits supporting surface, and a metal trim strip bridging the edge of theback-up plate and the edge of the composite plate and sealed thereto. 3.A composite metal plate surface heating unit as recited in claim 2 withthe addition of a reflector pan assembled beneath the back-up plate, theperipheral edge of the reflector pan being provided with an insulatinggasket means which is sandwiched between the reflector pan and back-upplate and serves as a heat transfer barrier therebetween said gasketmeans also being adapted to serve as the support means of the heatingunit on a support surface and thereby adapted to serve as a sealingmeans therebetween and to prevent direct contact of the composite platewith the support surface.
 4. A composite metal plate surface heatingunit having a thin multilayer composite metal sheet as its toputensil-supporting surface, said composite sheet having an inner heatspreading core of non-ferrous metallic alloy of high thermalconductivity, the core being sealed in an outer metallic alloy skin ofhigher strength and resistance to oxidation than the inner core, a metalsheathed electrical resistance heating element pressed against theunderside of the composite sheet to serve as the heat source for theheating unit, a metal back-up plate beneath the heating element forholding the heating element in place, the periphery of the back-up plateextending outwardly beyond the extremity of the inner core by a widemargin so as to reduce the conduction of heat from the heating unit toits supporting surface, and a metal trim encircling the heating unit andsealed between the edge of the top skin of the composite sheet and tothe edge of the back-up plate so as to stop the heat spreading coreshort of the periphery of the heating unit and reduce the conduction ofheat from the inner core to the peripheral extremity of the heatingunit.
 5. A composite metal plate surface heating unit as recited inclaim 4 wherein the extent of the bottom skin of the composite sheetsubstantially coincides with the extent of the inner core, and thediameter of the top skin substantially equals the diameter of theback-up plate.
 6. A composite metal plate surface heating unit asrecited in claim 5 with the addition of a reflector pan assembledbeneath the back-up plate, the peripheral edge of the reflector panbeing provided with an insulating gasket means which is sandwichedbetween the reflector pan and back-up plate and serves as a heattransfer barrier therebetween said gasket means also being adapted toserve as the support means of the heating unit on a support surface andthereby adapted to serve as a sealing means therebetween and to preventdirect contact of the composite plate with the support surface.
 7. Acomposite metal plate surface heating unit as recited in claim 4 whereina narrow annular margin of both the bottom skin and the inner core hasbeen removed from the top skin so that the periphery of the inner coreis set back from the periphery of the heating unit.
 8. A composite metalplate surface heating unit as recited in claim 4 wherein the peripheryof the composite sheet is pressed into a tapered bevelled eDge, a narrowstrip of the periphery of the back-up plate is formed to lie insubstantially the same plane as the bevelled edge of the compositesheet, whereby the said trim strip serves as an extension of thecomposite sheet.
 9. A composite metal plate surface heating unit asrecited in claim 8 with the addition of a reflector pan assembledbeneath the back-up plate, the peripheral edge of the reflector panbeing provided with an insulating gasket means which is sandwichedbetween the reflector pan and back-up plate and serves as a heattransfer barrier therebetween said gasket means also being adapted toserve as the support means of the heating unit on a support surface andthereby adapted to serve as a sealing means therebetween and to preventdirect contact of the composite plate with the support surface.